The present invention relates to titanium powder manufactured by crushing and grinding titanium sponge produced by metallo-thermic reduction of titanium chlorides. More particularly, the invention is directed to the cost-cutting and energy-saving manufacture of titanium powder by the improved process of magnesium-reduction of TiCl4 including vacuum separation (vacuum distillation) from magnesium and magnesium chlorides followed by the improved process of grinding and hydro-metallurgical treating of the ground sponge.
Titanium powder for commercial use, is presently produced by a hydride-dehydride (HDH) process, as disclosed in U.S. Pat. No. 6,168,644, by gas atomization, or by the plasma-rotating electrode process, as disclosed in U.S. Pat. No. 6,136,060. Raw materials for HDH process are titanium metal obtained by re-melting and processing titanium sponge, or ready-crushed titanium sponge itself, as disclosed in JP 10096003, 1998. These raw materials are hydrogenated, then, the brittle hydrogenated titanium is ground to the desired powder size that is dehydrogenated by vacuum heating. Essentially, the titanium powder production is a multi-step, energy-consumable, high-cost industrial process including the manufacture of titanium sponge, which is the most expensive part of the technology.
Numerous disclosures for magnesium-reducing TiCl4 and subsequent processing of the obtained titanium sponge are present in the art, starting from U.S. Pat. No. 2,205,854 granted to Wilhelm Kroll in 1940. Most developments were directed to improve the quality of the sponge by diminishing the final content of magnesium, chlorine, oxygen, and iron contaminants. Various processes have been developed during the last two decades for energy-saving, cost-effective, sponge-related technologies.
For example, Russian patent 2,061,585, 1994, describes the manufacture of titanium powder by (a) magnesium-thermic reduction of titanium chlorides in a reactor, (b) preliminary distillation of the reaction mass to the content of magnesium chloride of 5-12%, (c) cooling of obtained sponge block in argon, (d) crushing and grinding the sponge into the powder having a particle size of 0-12 mm, (e) preliminary drying of the powder at  less than 250xc2x0 C., (f) cooling and additional grinding, (g) final distillation of the powder from magnesium chloride residues by vacuum separation, (h) hydro-metallurgical treatment, (i) final drying, and (j) final grinding of titanium powder.
In spite of saving time and energy of sponge production, this process is not cost-effective when considering titanium powder as the final product. In this process, the first stage of vacuum separation is carried out at 1020xc2x0 C., which results in a solid sintered block of the reaction mass and increases the time of sponge distillation. Double-stage vacuum separation accompanied by multi-stage drying and grinding increases the process time and electric energy consumption, and significantly decreases the powder productivity. Besides, multi-stage hot drying increases the content of gaseous impurities in the obtained powder.
Periodic removal of exhaust magnesium chloride from the reactor bottom and cooling a reaction interface by argon flow (disclosed in JP 59001646, 1984) reduced the time of sponge production, but neither the cost nor the energy of the entire process of powder manufacture is gained.
The same result, insignificant to powder cost, was reached in the process disclosed in JP 61012836, 1986 which increases the sponge yield by predetermined blowing of TiCl4 at the temperature of  less than 600xc2x0 C. under argon into molten magnesium.
The electric power consumption was decreased by 20% using a condensing vessel in the reactor for removing unreacted magnesium and residual magnesium chloride from the reaction zone as disclosed in JP 03047929, 1991. This energy savings related only to sponge production and does not reflect on the total production cost because the obtained ductile sponge needs to be hydrated/dehydrated with the repetition of the multi-stage processing.
An attempt at producing titanium powder directly by the magnesium-thermic reduction of TiCl4 and eliminated all expenses involved with sponge production was made by Uda T. with colleagues (2nd Int. Conf on Process. Mater. and Properties, TMS, 2000, p. 31-36). This method looks promising for the future but presently, it is far from an industrial scale. Incidentally, some rather expensive rare-earth metals (e.g., Dy and Ho) are involved in the process.
Productivity of the magnesium-thermic process was increased by the preliminary cleaning of TiCl4 and accelerated the supply into the reactor as disclosed in Russian patent 2,145,979, 2000. This method also related only to the sponge production and results mostly in the sponge quality.
A way of accelerating the distillation stage was offered by Sandier R. A. and Kholmovskaya N. A. (Izv. Akad Nauk USSR, Met., 1967, 6, p. 58-62). According to this, the oxide impurities are partially soluble in fused MgCl2 at a higher temperature, therefore the reduction process should be carried out at more elevated temperature and simultaneously increase feeding the reactor with TiCl4 to obtain a porous titanium sponge, which facilitates the removal of fused MgCl2 together with oxygen dissolved in it. Unfortunately, the higher temperature results in additional power consumption.
The supply of hot argon through the reaction mass can also speed up the distillation process by vaporizing the magnesium and magnesium chloride in gaseous form, as disclosed in the U.S. Pat. No. 3,880,652. But additional expenses involved with heating and supplying high-temperature argon override the savings on production cost during the distillation stage.
The manufacture of high-purity titanium sponge lumps is disclosed in recent JP 2001262246, 2001. The process includes crushing the titanium sponge to a particle size of 2-50 mm and heat-treating at a reduced argon pressure of 600-1100xc2x0 C. Crushing and heat treatment are repeated several times until the desired purity of coarse titanium is reached. This method is ineffective for commonly used titanium, and requires HDH processing to obtain the powder for industrial purposes.
All other known methods of producing titanium powder directly from magnesium-reduced sponge have the same drawback: cost and energy savings are only realized for one or two stages, but not for the continuous multi-stage process, which makes none of these processes cost effective.
Not one conventional process comprises the sponge production adjusted specially to subsequent powder manufacture: sponge lumps are ductile and need to be treated by HDH process.
The object of the invention is to establish a continuous cost-effective process to produce as-reduced titanium powder from titanium sponge obtained by the magnesium-thermic process specially adjusted to subsequent powder manufacturing.
Another objective of the present invention is to control the structure of the reaction mass block to facilitate and accelerate the sponge distillation from magnesium and magnesium chloride residues.
It is yet another objective to produce brittle sponge metal to provide crushing lumps and grinding titanium powder with additional HDH processing.
Another objective of the invention is to find energy-saving combinations of the process stages to achieve a cost effective method for the entire technology.
The nature, utility, and further features of this invention will be more apparent from the following detailed description with respect to preferred embodiments of the invented technology.
The invention relates to the manufacture of titanium powder by magnesium-thermic reduction of titanium chlorides followed by thermal-vacuum distillation, crushing, grinding. and hydro-metallurgical treatment of the obtained titanium sponge. While the use of magnesium-thermic reduced sponge has previously been contemplated in the titanium powder production as mentioned above, problems related to cost-effectiveness, energy saving, and adjusting the sponge production to facilitate powder manufacturing have not been resolved.
The invention overcomes these problems by (a) magnesium-thermic reduction of titanium chlorides performed in such a way that results in the formation of a hollow block of the reaction mass having an open cavity in the center of the block, (b) thermal-vacuum separation of the hollow block at 850-950xc2x0 C. and residual pressure of 10xe2x88x922-10xe2x88x923 mm, (c) cooling of the titanium hollow block in a H2-contained atmosphere at excessive hydrogen pressure, (d) crushing the hydrogenated titanium block, (e) grinding the crushed titanium pieces into the powder simultaneously with a hydro-metallurgical treatment of obtained titanium powder in a diluted liquid solution of at least one chloride selected from: magnesium chloride, sodium chloride, potassium chloride, or titanium chloride, and (f) drying, and optionally dehydrating the titanium powder ground to a predetermined size.
The formation of the hollow block of the reaction mass with the open cavity in the center of the block is carried out by increasing the reaction mass on the inside surface of the reactor.
The hydro-metallurgical treatment of titanium powder is carried out in the solutions having the total content of chlorides of 0.5-10 wt. %, at the powder-to-solution weight ratio from 1:1 to 1:4.
Cooling of the titanium hollow block in the hydrogen-containing atmosphere is carried out to the temperature of 550-450xc2x0 C. at the H2 excessive pressure of 0.2 bar or higher.
The hydrogen-contained atmosphere is the gaseous mixture of hydrogen with argon and/or helium.
In essence, the core of the invention is the combination and adjustment of operations directed to titanium sponge production with operations directed to titanium powder production. So, (1) cooling of the reaction block after vacuum distillation is combined with its hydrogenation, (2) the magnesium-thermic reduction is adjusted to subsequent distillation and hydrogenation by forming the hollow block of the reaction mass, (3) hydro-metallurgical treatment of the sponge is combined with powder grinding, and finally, (4) drying of ground titanium powder is combined with dehydrogenation. In other words, the HDH process is included in the process of magnesium-thermic sponge production.
Therefore, the innovative technology results in saving energy, significantly decreases the number of processing stages, and cuts production costs.
High productivity and energy saving of sponge processing and increasing the quality of titanium powder with respect to its chemical composition and particle size distribution, are achieved by the intensification of each stage of the technology: formation of the hollow block of the reaction mass with an open cavity in the center of the block, vacuum separation at lower temperature, acceleration of the block cooling, and a combination of sponge grinding with the hydro-metallurgical treatment of the powder.
In our innovative process, the magnesium-thermic reduction of the titanium chlorides is carried out at 750-860xc2x0 C. in an inert atmosphere in the reactor partially filled with liquid magnesium at a controlled supply of TiCl4 with maximal rate to cut the process duration. The reaction mass is formed on the inner surface of the reactor, in which the surface is permanently contacted with molten magnesium. These process conditions result in the growth of the reaction mass on the inner surface of the reactor and subsequently, in the formation of the hollow block of the reaction mass having the open cavity in the center. Such shape of the reaction mass provides a high rate of magnesium reduction, that accelerates the formation of the porous block, and decreases the total duration of the sponge production process. A shorter time of the process results in the significant savings of supplied electric power.
The block obtained on the reduction stage is subjected to thermal-vacuum separation at 850-950xc2x0 C. and the starting pressure of 10xe2x88x922-10xe2x88x923 mm Hg. Evaporation of magnesium and magnesium chlorides happen from both inner and exterior surfaces of the reaction mass block. The open cavity in the center of the block and its developed porosity allow (1) to accelerate the vacuum separation of magnesium and magnesium chloride at the cost of increase in the evaporation surfaces, and (2) to carry out the vacuum separation at lower temperature.
The vacuum separation is finished when the pressure in the reactor reaches the value of 10xe2x88x922-10xe2x88x923 mm Hg again. At this moment, an inflow of air is stopped to prevent any oxidation of the obtained sponge and gas atmosphere.
The sponge block is cooled down from 550-450xc2x0 C. in the hydrogen-argon gaseous mixture having the pressure gauge of 0.2 bar. Then, the reactor is outgassed, filled with argon, and cooled down to  less than 100xc2x0 C. Cooling of the sponge block after the distillation is also accelerated, initially caused by a hydrogen-argon flow, and then caused by greater contact surface of the block.
Cooling in the hydrogen-containing atmosphere is accompanied with the hydration of the entire mass of the sponge block that facilitates the subsequent crushing and grinding of the sponge as well as reduces time of the hydro-metallurgical treatment of titanium powder. Hydrated sponge increases the yield of dispersed titanium powder during grinding to improve its uniformity and quality. Crushing and grinding of the hydrated sponge is carried out for only one run, which significantly reduces the electric power consumption as compared to the conventional multi-run grinding of ductile titanium sponge.
Technically, the cold sponge hydrated to 1-3 wt. % of H2 is crushed to coarse grains having an average size up to 5 mm. Then, the coarse titanium is ground in a ball mill filled with aqueous solutions of magnesium chloride, sodium chloride, potassium chloride, or titanium chloride. The weight ratio of titanium powder to steel balls is 1:(4-8).
The combination of grinding with the hydro-metallurgical treatment of titanium powder in diluted chloride solutions also results in a savings of electric power consumption and increased productivity. The chloride concentration in these solutions is limited from 0.5 wt. % on the low side to 10 wt. % on the high side. If the chloride concentration is below 0.5 wt. %, the passivity of the powder does not occur. Exceeding chloride concentration over 10 wt. % is not reasonable because a partial dissolution of titanium powder may occur, and a part of the final product will be lost. The powder-to-solution weight ratio from 1:1 to 1:4 was established experimentally based on the value and the rate of magnesium leaching.
Finally, the obtained titanium powder is dried and, optionally dehydrated in a vacuum.